1. Field of the Invention
The present invention relates to an iris recognition system, and particularly to a method for adjusting a camera focus precisely on an iris of a user for increasing the user's convenience and for obtaining a more accurate iris image of the user. More particularly, the present invention relates to a focus position adjusting apparatus and method in an iris recognition system, which enables to adjust the distance between the user and the camera and focus angle between the user and the camera more accurately.
2. Description of the Related Art
As well known already, there have been a number of systems for security, crime prevention, and identity authentication, such as the traditional contact cards system or the non-contact cards system and up to the fingerprint recognition system. The iris recognition system has certainly joined this stream for authenticating a person's identity before allowing or rejecting the person to enter a particular place or to access specific data.
Among those, the iris recognition system is considered to be the best for its high recognition rate compared with the fingerprint recognition, and for its high accuracy. The iris recognition system is a technique for authenticating a person by comparing a pre-registered iris data with a new iris data that has been prepared by capturing iris images using a video camera and making iris pattern features into data using an image process technique.
FIG. 1 is a schematic diagram of a general iris recognition system in a related art.
With reference to FIG. 1, operation of the iris recognition system is now explained below.
As a user approaches the iris recognition system, a distance measurement sensor 109 measures the distance between the user to the system, and a controller 105, having received the distance measurement value through an actuator 107, decides whether the distance measurement value is within the operation limit.
If it turns out that the user is within the operation limit, a control signal is sent out to the actuator 107 to extract iris images. And, the actuator 107 sends an active signal to an external indicator 108 and lets the user know that the system is on. When the user puts his or her eyes on an optical axis of a camera 103 through an optical window 101, a cold mirror 102 blocks a visible ray and passes infrared rays.
And, the system indicates whether the iris of the user should be placed to make sure the user's eyes are properly positioned on the optical axis of the camera 103.
The control device 105, on the other hand, is provided with the distance from the distance measurement sensor 109 to the user, and based on the distance measurement value, it calculates zoom and focus values of the camera 103 and performs zoom in/zoom out and focusing control. Later, the control device 105 adjusts the intensity of an illumination device 106 through the actuator 107 in accordance with the distance measurement value, and photographs the iris image using the camera 103.
The photographed iris image goes through a signal process to be appropriate for the iris image analysis at a frame grabber 104, and based on the information about the processed iris image, the control device 105 recognizes the iris and decides whether or not to authenticate the user.
The performance of this iris recognition system is totally dependent on how fast and how accurately it can recognize the iris.
There are actually a few techniques of extracting the iris image in order to photograph the iris of the user from an appropriate distance. For example, sometimes the user himself has to focus the camera by looking at the screen and moving back and forth, or in some cases, several cameras are used at one time to find out where the user's face and eyes are and photograph the user's iris image. Also, some obtain the iris image by using the distance measurement sensor which measures the distance between the camera and the user in order to focus the camera automatically.
First of all, it would be pointless to say that the user would feel uncomfortable if he personally has to move around within a certain distance to focus the camera, while looking at the screen. Also, in this case, a single light source is used. Therefore, if the user wears glasses, the reflected image from the glasses makes it difficult to catch more accurate iris images.
To prevent such problem, the user should keep moving while looking at the screen for himself until no reflection occurs, increasing inconvenience to the user.
Fortunately, using several cameras to focus the camera and obtain iris images has somewhat solved the trouble the user had to go through. But this time, the equipment is very complicated for a normal person to operate and it required very sophisticated control. In other words, the system uses two cameras for finding out where the user's face and eyes are, and another camera for obtaining the iris image.
Although the system is convenient to use in that the user does not have to focus his eyes personally for the iris recognition because the system automatically focuses the camera and catches the iris image, the system configuration itself is very complicated in order to use several cameras and operate each camera systematically and electrically,
Lastly, in case the distance measurement sensor is used to focus the camera and photograph iris images, the distance measurement sensor senses a person's approach and focuses the camera based on the inputted images in possession and the focus values outputted from the camera.
However, since this technique also uses a single light source, the reflection problem due to the glasses of the user is likely to happen any time. As an attempt to avoid the secondary reflex due to the glassed, three LED (light-emitting diode) illuminations were put on the left side, the right side, and the upper side. But it was still uncomfortable to use because one should keep changing positions of the illuminations to get the images.
FIG. 2 is a block diagram of an autofocus adjusting device using a distance measurement sensor in the prior art.
As shown in the drawing, a distance measurer 202 measures the distance between the user and the camera 205 at designated regular time intervals using the distance measurement sensor 201, and outputs the distance information successively. A distance processor 203, using the distance information, catches characteristics of the user's movement. More specifically, based on that successive distance information, the distance processor 203 measures the user's movement speed. If the speed is a positive number (+), it means that the user is approaching, and if the speed is a negative number (−), it means the user is going away, and if the absolute speed is within the limit, it means the user stopped moving.
A camera operation controller 204, using the information about distance, speed and acceleration provided from the distance processor 203, controls the operation of the camera 205 when the use stands still. Here, even when the user's movement is not yet stabilized, it is important to estimate beforehand where the user is going stop and drive the camera's lens to that position because it certainly reduces time necessary for focusing the camera.
When the user's movement is stabilized, the camera operation controller 204 adjusts the camera's zoom and focus based on the distance measurement values. Considering that the user can't be perfectly still but keeps moving little bit and the measured distance values are not necessarily the actual distances to the user's eyes, it is rather natural to accept the possibility of measurement error to a certain degree. Therefore, a fine adjustment process is carried out involving the camera operation controller 204, in which the camera operation controller focuses the camera by analyzing the successively inputted iris image from an image controller 206, calculating a focus range therefrom, moving a zoom and focus lens until the focus range becomes appropriate for performing authentication, and continuing the tracking until a maximum value is obtained.
However, if the user is wearing glasses, the iris image of the user could be reflected in accordance with the angle between the glasses and the LED mounted at an illuminator 208. To prevent this problem, the image processor 206 detects a possible reflection degree before calculating the focus range, and outputs the glasses reflection information to an illumination controller 207.
In a way of avoiding the glasses' reflection, the illumination controller 207 controls the lighting condition of the illumination LED based on the glasses reflection information, and changes the reflected positions from the glasses as well. In this manner, the reflection by the glasses can be prevented and the iris image recognition can be done successfully through an analysis on the iris images obtained from the camera 206.
However, one problem of the system is that it depends too heavily on the distance measurement sensor to measure the motion direction and distance of the lens when the camera needs to be focused. Thus, if the distance measurement sensor does not give accurate information on the distance to the user's eyes, which unfortunately does occur very often, the motion direction of the lens could be designated to a wrong direction and the time for adjusting the focus might take longer than expected. In addition, since the user has to approach within the permitted limit of the iris recognition system, the system is not that convenient for the user.
On the other hand, according to the traditional iris recognition system for use of the video conference, to recognize the user's iris, the user has to put his eyes on a position where the distance and the focus adjusting image (using two points) in the iris recognition camera lens are conformed with each other. Once the user gazes the point where two points in the camera converge, the system starts the iris recognition.
However, putting the two points together in the system described above works conveniently for the user only when the iris recognition camera is already being focused, but since the system uses a single focus lens, the user sometimes has to focus the camera if necessary. Therefore, the system is not that convenient to use especially when the iris recognition camera is not focused because the user has to not only adjust the distance between the iris recognition camera and him but also conform the two points in the camera.
That is to say, the system gives inconvenience to the user, making him move to a position where two points in a small lens conform to each other while looking at the camera lens.
Accordingly, an iris recognition apparatus needs to be developed, which enables to measure the distance between the user and the camera more accurately, more conveniently, and more quickly, and to focus the camera automatically.
FIG. 3 is a diagram explaining a relation between the iris recognition camera and the user in terms of position and distance.
As depicted in the drawing, the iris recognition system requires the user to adjust the focal distance (D) and the focal angle accurately while watching the iris recognition camera to get desired iris images.
The focal distance (D) is Z operating range between user and device, and the focal range is X-Y operating range in FIG. 3.
According to the system shown in FIG. 4, the user is supposed to put his eyes on the place where the distance and the focus adjusting image in the iris recognition camera with a single focus lens (use two circles with different colors) conform to each other. In short, the system does not start iris recognition until the user looks at the place where two points in the camera converge.
In the present context, the term focus position is intended to indicate that the user's position which can acquire image to recognize iris. For a better adjustment of the focus position, the user is recommended to keep a certain distance from the camera at a certain distance (i.e., 44 cm to 48 cm), and is encouraged to adjust the focal angle using a blue circle and a white circle in the camera lens.
In other words, the user is supposed to keep looking at the camera and move towards where he can adjust the focal angle until the two circles become one.
FIG. 4(a) illustrates a case where the focal angle is adjusted and (b) illustrates a case where the focal angle went wrong.
However, the apparatus encourages the user to practice to get the feeling of the focus position beforehand using a tapeline or something until he becomes intuitively accustomed to the focus position to a certain level. But for the user, it is rather difficult and inconvenient to adjust the focus position, making the white circle out of those two circles looking in the camera lens become one with the blue circle at the same time. Considering the small sized lens and visual difference of the user's eyes, the task seems to be even harder.
Moreover, because the system uses two lenses and the distance between the LED and the lens is very short, the user, even when he is not at the right front of the lens, could see the LED light, so he cannot be sure whether the focal angle is properly adjusted or not. Further, there is a white point marked on the surface of the lens such that the user can see the LED light from any angle and focus, but this can be an obstacle to obtain good iris images. On top of boring a hole in the reflex mirror to transmit the LED light, if the user looks at the iris recognition camera from a different angle rather than the front, it is very hard to adjust the focal angle since the camera would not look like a circle to the user then.